Heterogeneity of the angiogenic response induced in different normal adult tissues by vascular permeability factor/vascular endothelial growth factor

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is an angiogenic cytokine with potential for the treatment of tissue ischemia. To investigate the properties of the new blood vessels induced by VPF/VEGF, we injected an adenoviral vector engineered to express murine VPF/VEGF164 into several normal tissues of adult nude mice or rats. A dose-dependent angiogenic response was induced in all tissues studied but was more intense and persisted longer (months) in skin and fat than in heart or skeletal muscle (< or =3 weeks). The initial response (within 18 hours) was identical in all tissues studied and was characterized by microvascular hyperpermeability, edema, deposition of an extravascular fibrin gel, and the formation of enlarged, thin-walled pericyte-poor vessels ("mother" vessels). Mother vessels developed from preexisting microvessels after pericyte detachment and basement membrane degradation. Mother vessels were transient structures that evolved variably in different tissues into smaller daughter vessels, disorganized vessel tangles (glomeruloid bodies), and medium-sized muscular arteries and veins. Vascular structures closely resembling mother vessels and each mother vessel derivative have been observed in benign and malignant tumors, in other examples of pathological and physiological angiogenesis, and in vascular malformations. Together these data suggest that VPF/VEGF has a role in the pathogenesis of these entities. They also indicate that the angiogenic response induced by VPF/VEGF is heterogeneous and tissue specific. Finally, the muscular vessels that developed from mother vessels in skin and perimuscle fat have the structure of collaterals and could be useful clinically in the relief of tissue ischemia.

Neutrophils emigrate from venules by a transendothelial cell pathway in response to FMLP

Circulating leukocytes are thought to extravasate from venules through open interendothelial junctions. To test this paradigm, we injected N-formyl-methionyl-leucyl-phenylalanine (FMLP) intradermally in guinea pigs, harvesting tissue at 5-60 min. At FMLP-injected sites, venular endothelium developed increased surface wrinkling and variation in thickness. Marginating neutrophils formed contacts with endothelial cells and with other neutrophils, sometimes forming chains of linked leukocytes. Adherent neutrophils projected cytoplasmic processes into the underlying endothelium, especially at points of endothelial thinning. To determine the pathway by which neutrophils transmigrated endothelium, we prepared 27 sets of serial electron microscopic sections. Eleven of these encompassed in their entirety openings through which individual neutrophils traversed venular endothelium; in 10 of the 11 sets, neutrophils followed an entirely transendothelial cell course unrelated to interendothelial junctions, findings that were confirmed by computer-assisted three-dimensional reconstructions. Having crossed endothelium, neutrophils often paused before crossing the basal lamina and underlying pericytes that they also commonly traversed by a transcellular pathway. Thus, in response to FMLP, neutrophils emigrated from cutaneous venules by a transcellular route through both endothelial cells and pericytes. It remains to be determined whether these results can be extended to other inflammatory cells or stimuli or to other vascular beds.

Vascular permeability factor/vascular endothelial growth factor and the significance of microvascular hyperpermeability in angiogenesis

This Chapter has reviewed the literature concerning VPF/VEGF as a potent vascular permeabilizing cytokine. In accord with this important role, microvessels have been found to be hyperpermeable to plasma proteins and other circulating macromolecules at sites where VPF/VEGF and its receptors are overexpressed, i.e., in tumors, healing wounds, retinopathies, many important inflammatory conditions and in certain physiological processes, such as ovulation and corpus luteum formation. Moreover, microvascular hyperpermeability to plasma proteins was shown to have an important consequence: the laying down of a fibrin-rich extracellular matrix. This provisional matrix, in turn, favors and supports the ingrowth of fibroblasts and endothelial cells which, together, transform the provisional matrix into the mature stroma characteristic of tumors and healed wounds. Finally, we have considered the pathways by which these and other circulating macromolecules cross the endothelium of normal and VPF/VEGF-permeabilized microvessels. These pathways include VVOs and trans-endothelial openings that have been variously interpreted as inter-endothelial cell gaps or trans-endothelial cell pores. At least some trans-endothelial cell pores may arise from VVOs. In conclusion, these data provide new insights into the mechanisms of angiogenesis and stroma formation, insights which are potentially applicable to a wide variety of disease states and which may lead to identification of new targets for therapeutic intervention.

Vesiculo-vacuolar organelles and the regulation of venule permeability to macromolecules by vascular permeability factor, histamine, and serotonin

In contrast to normal microvessels, those that supply tumors are strikingly hyperpermeable to circulating macromolecules such as plasma proteins. This leakiness is largely attributable to a tumor-secreted cytokine, vascular permeability factor (VPF). Tracer studies have shown that macromolecules cross tumor vascular endothelium by way of a recently described cytoplasmic organelle, the vesiculo-vacuolar organelle or VVO (VVOs are grapelike clusters of interconnected, uncoated vesicles and vacuoles). However, equivalent VVOs are also present in the cytoplasm of normal venules that do not leak substantial amounts of plasma protein. To explain these findings, we hypothesized that VPF increased the permeability of tumor blood vessels by increasing VVO function and that the VVOs of normal venules were relatively impermeable in the absence of VPF stimulation. To test this hypothesis, VPF was injected intradermally in normal animals after intravenous injection of a soluble macromolecular tracer, ferritin, whose extravasation could be followed by electron microscopy. VPF caused normal venules to leak ferritin, and, as predicted by our hypothesis, ferritin extravasated by way of VVOs, just as in hyperpermeable tumor microvessels. Ultrathin (14-nm) serial electron microscopic sections and computer-aided three-dimensional reconstructions better defined VVO structure. VVOs occupied 16-18% of endothelial cytoplasm in normal venules. Individual VVOs were clusters of numerous (median, 124) interconnected vesicles and vacuoles that formed complex pathways across venular endothelium with multiple openings to both luminal and abluminal surfaces. Like VPF, histamine and serotonin also stimulated ferritin extravasation across venules by way of VVOs. Together, these data establish VVOs as the major pathway by which soluble plasma proteins exit venules in response to several mediators that increase venular hyperpermeability. These same mediators also increased the extravasation of colloidal carbon, but this large particulate nonphysiological tracer exited venules primarily through endothelial gaps.

The vesiculo-vacuolar organelle (VVO). A new endothelial cell permeability organelle

A newly defined endothelial cell permeability structure, termed the vesiculo-vacuolar organelle (VVO), has been identified in the microvasculature that accompanies tumors, in venules associated with allergic inflammation, and in the endothelia of normal venules. This organelle provides the major route of extravasation of macromolecules at sites of increased vascular permeability induced by vascular permeability factor/vascular endothelial growth factor (VPF/VEGF), serotonin, and histamine in animal models. Continuity of these large sessile structures between the vascular lumen and the extracellular space has been demonstrated in kinetic studies with ultrastructural electron-dense tracers, by direct observation of tilted electron micrographs, and by ultrathin serial sections with three-dimensional computer reconstructions. Ultrastructural enzyme-affinity cytochemical and immunocytochemical studies have identified histamine and VPF/VEGF bound to VVOs in vivo in animal models in which these mediators of permeability are released from mast cells and tumor cells, respectively. The high-affinity receptor for VPF/VEGF, VEGFR-2, was localized to VVOs and their substructural components by pre-embedding ultrastructural immunonanogold and immunoperoxidase techniques. Similar methods were used to localize caveolin and vesicle-associated membrane protein (VAMP) to VVOs and caveolae, indicating a possible commonality of formation and function of VVOs to caveolae.

Increased platelet aggregability associated with platelet GPIIIa PlA2 polymorphism: the Framingham Offspring Study

The platelet glycoprotein IIb/IIIa (GP IIb/IIIa) plays a pivotal role in platelet aggregation. Recent data suggest that the PlA2 polymorphism of GPIIIa may be associated with an increased risk for cardiovascular disease. However, it is unknown if there is any association between this polymorphism and platelet reactivity. We determined GP IIIa genotype and platelet reactivity phenotype data in 1422 subjects from the Framingham Offspring Study. Genotyping was performed using PCR-based restriction fragment length polymorphism analysis. Platelet aggregability was evaluated by the Born method. The threshold concentrations of epinephrine and ADP were determined. Allele frequencies of PlA1 and PlA2 were 0.84 and 0.16, respectively. The presence of 1 or 2 PlA2 alleles was associated with increased platelet aggregability as indicated by incrementally lower threshold concentrations for epinephrine and ADP. For epinephrine, the mean concentrations were 0.9 micromol/L (0.9 to 1.0) for homozygous PlA1, 0.7 mmol/L (0.7 to 0.9) for the heterozygous PlA1/PlA2, and 0.6 micromol/L (0.4 to 1.0) for homozygous PlA2 individuals, P=0.009. The increase in aggregability induced by epinephrine remained highly significant (P=0.007) after adjustment for covariates. For ADP-induced aggregation, the respective mean concentrations were 3.1 micromol/L (3.0 to 3.2), 3.0 micromol/L (2.9 to 3.2), and 2.8 micromol/L (2.4 to 3.3); P=0.19 after adjustment for covariates. Our findings indicate that molecular variants of the gene encoding GP IIIa play a role in platelet reactivity in vitro. Our observations are compatible with and provide an explanation for the reported association of the PlA2 allotype with increased risk for cardiovascular disease.

Glomeruloid microvascular proliferation follows adenoviral vascular permeability factor/vascular endothelial growth factor-164 gene delivery

Glomeruloid bodies are a defining histological feature of glioblastoma multiforme and some other tumors and vascular malformations. Little is known about their pathogenesis. We injected a nonreplicating adenoviral vector engineered to express vascular permeability factor/vascular endothelial growth factor-164 (VPF/VEGF(164)) into the ears of athymic mice. This vector infected local cells that strongly expressed VPF/VEGF(164) mRNA for 10 to 14 days, after which expression gradually declined. Locally expressed VPF/VEGF(164) induced an early increase in microvascular permeability, leading within 24 hours to edema and deposition of extravascular fibrin; in addition, many pre-existing microvessels enlarged to form thin-walled, pericyte-poor, "mother" vessels. Glomeruloid body precursors were first detected at 3 days as focal accumulations of rapidly proliferating cells in the endothelial lining of mother vessels, immediately adjacent to cells expressing VPF/VEGF(164). Initially, glomeruloid bodies were comprised of endothelial cells but subsequently pericytes and macrophages also participated. As they enlarged by endothelial cell and pericyte proliferation, glomeruloid bodies severely compromised mother vessel lumens and blood flow. Subsequently, as VPF/VEGF(164) expression declined, glomeruloid bodies devolved throughout a period of weeks by apoptosis and reorganization into normal-appearing microvessels. These results provide the first animal model for inducing glomeruloid bodies and indicate that VPF/VEGF(164) is sufficient for their induction and necessary for their maintenance.

Noninvasive quantification of the cerebral metabolic rate for glucose using positron emission tomography, 18F-fluoro-2-deoxyglucose, the Patlak method, and an image-derived input function

The authors developed and tested a method for the noninvasive quantification of the cerebral metabolic rate for glucose (CMRglc) using positron emission tomography (PET), 18F-fluoro-2-deoxyglucose, the Patlak method, and an image-derived input function. Dynamic PET data acquired 12 to 48 seconds after rapid tracer injection were summed to identify carotid artery regions of interest (ROIs). The input function then was generated from the carotid artery ROIs. To correct spillover, the early summed image was superimposed over the last PET frame, a tissue ROI was drawn around the carotid arteries, and a tissue time activity curve (TAC) was generated. Three venous samples were drawn from the tracer injection site at a later time and used for the spillover and partial volume correction by non-negative least squares method. Twenty-six patient data sets were studied. It was found that the image-derived input function was comparable in shape and magnitude to the one obtained by arterial blood sampling. Moreover, no significant difference was found between CMRglc estimated by the Patlak method using either the arterial blood sampling data or the image-derived input function.

Genetic and environmental contributions to platelet aggregation: the Framingham heart study

BACKGROUND

Platelet aggregation plays an important role in arterial thrombosis in coronary heart disease, stroke, and peripheral arterial disease. However, the contribution of genetic versus environmental influences on interindividual variation in platelet aggregability is poorly characterized.

METHODS AND RESULTS

We studied the heritability of platelet aggregation responses in 2413 participants in the Framingham Heart Study. The threshold concentrations of epinephrine and ADP required to produce biphasic platelet aggregation and collagen lag time were determined. Mixed-model linear regression was used to calculate correlation coefficients within sibships and within spouse pairs. Variance and covariance component methods were used to estimate the proportion of platelet aggregation attributable to measured covariates versus additive genetic effects. After accounting for environmental covariates, the adjusted sibling correlations for epinephrine, ADP, and collagen lag time were 0.24, 0.22, and 0.31, respectively (P=0.0001 for each). In contrast, adjusted correlations for spouse-pairs were -0.01, 0.05, and -0.02, respectively (all P>0.30). The estimated heritabilities were 0.48, 0.44, and 0.62, respectively. Measured covariates accounted for only 4% to 7% of the overall variance in platelet aggregation, and heritable factors accounted for 20% to 30%. The platelet glycoprotein IIIa Pl(A2) polymorphism and the fibrinogen Hind III beta-148 polymorphism contributed <1% to the overall variance.

CONCLUSIONS

In our large, population-based sample, heritable factors play a major role in determining platelet aggregation, and measured covariates play a lesser role. Future studies are warranted to identify the key genetic variants that regulate platelet function and to lay the groundwork for rational pharmacogenetic approaches.

Models for computer simulation studies of input functions for tracer kinetic modeling with positron emission tomography

In tracer kinetic modeling with Positron Emission Tomography (PET), the direct measurement (piecewise linear approximation) of plasma time-activity curve of tracer (PTAC) is often used as the input function to estimate regional physiological parameters. However, no explicit general model is available for PTAC itself, which limits the further study of the effects of PTAC, such as PTAC measurement noise or PTAC sampling schedules, on the physiological parameters estimation. A PTAC model is proposed in this paper and compared with other four possible candidates. Eight sets of [18F]-fluoro-2-deoxy-D-glucose (FDG) experimental data were used to test the models and several statistical criteria were used to validate their adequacy. An application of the model to improve the estimation of local cerebral metabolic rate of glucose (LCMRGlc) is presented. This model is also expected to be useful for generating realistic PTAC curves in computer simulation studies of other tracers and their kinetic modeling characteristics.

Identification of a PDZ-domain-containing protein that interacts with the scavenger receptor class B type I

The scavenger receptor class B type I (SR-BI) mediates the selective uptake of cholesteryl esters from high-density lipoprotein (HDL) and cholesterol secretion into bile in the liver. In this study, we identified an SR-BI-associated protein from rat liver membrane extracts by using an affinity chromatography technique. This protein of 523 amino acids contains four PDZ domains and associates with the C terminus of SR-BI by using its N-terminal first PDZ domain. Therefore, we denoted this protein as CLAMP (C-terminal linking and modulating protein). CLAMP was located mostly in the sinusoidal membranes, whereas SR-BI was detected in both sinusoidal and canalicular membranes. After the solubilization of the liver membranes with Triton X-100, SR-BI was immunoprecipitated with anti-CLAMP monoclonal antibody, suggesting the association of these proteins in vivo. By coexpressing SR-BI with CLAMP in Chinese hamster ovary cells, we observed (i) the increase in the expression level of SR-BI, (ii) the reduction in the deacylation rate of the cholesteryl esters taken up from HDL, and (iii) the change in the intracellular distribution of fluorescent lipid 1,1'-dioctadecyl-3,3, 3',3'-tetramethylindocarbocyanine percholate taken up from HDL. Taken together, these data suggest that CLAMP, a four-PDZ-domain-containing protein, is associated with SR-BI in the liver sinusoidal plasma membranes and may modulate the intracellular transport and metabolism of cholesteryl esters taken up from HDL.

Vascular permeability factor/vascular endothelial growth factor: a multifunctional angiogenic cytokine

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the endothelial cells lining nearby microvessels to proliferate, to migrate and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular endothelial cells hyperpermeable so that they spill plasma proteins into the extravascular space, leading to profound alterations in the extracellular matrix that favor angiogenesis. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of endothelial cell division and new blood vessel formation. It would seem, therefore, that tumors have made use of fundamental pathways that developed in multicellular organisms for purposes of tissue defense, renewal and repair. VPF/VEGF, therefore, has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important--perhaps essential--elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in sub-toxic concentrations that are more than sufficient to induce angiogenesis (Connolly et al., 1989a). Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating VPF/VEGF expression. In fact, there are already clear example of this. A number of putative angiogenic factors including small molecules (e.g. prostaglandins, adenosine) as well as many cytokines (e.g. TGF-alpha, bFGF, TGF-beta, TNF-alpha, KGF, PDGF) have all been shown to upregulate VPF/VEGF expression. Further studies that elucidate the crosstalk among various angiogenic factors are likely to contribute significantly to a better understanding of the mechanisms by which new blood vessels are formed in health and in disease.

The role of type I interferon production by dendritic cells in host defense

Type I interferons (IFN) and dendritic cells (DC) share an overlapping history, with rapidly accumulating evidence for vital roles for both production of type 1 IFN by DC and the interaction of this IFN both with DC and components of the innate and adaptive immune responses. Within the innate immune response, the plasmacytoid DC (pDC) are the "professional" IFN producing cells, expressing specialized toll-like receptors (TLR7 and -9) and high constitutive expression of IRF-7 that allow them to respond to viruses with rapid and extremely robust IFN production; following activation and production of IFN, the pDC subsequently mature into antigen presenting cells that help to shape the adaptive immune response. However, like most cells in the body, the myeloid or conventional DC (mDC or cDC) also produce type I IFNs, albeit typically at a lower level than that observed with pDC, and this IFN is also important in innate and adaptive immunity induced by these classic antigen presenting cells. These two major DC subsets and their IFN products interact both with each other as well as with NK cells, monocytes, T helper cells, T cytotoxic cells, T regulatory cells and B cells to orchestrate the early immune response. This review discusses some of the converging history of DC and IFN as well as mechanisms for IFN induction in DC and the effects of this IFN on the developing immune response.

Ultrastructural localization of the vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) receptor-2 (FLK-1, KDR) in normal mouse kidney and in the hyperpermeable vessels induced by VPF/VEGF-expressing tumors and adenoviral vectors

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) interacts with two high-affinity tyrosine kinase receptors, VEGFR-1 and VEGFR-2, to increase microvascular permeability and induce angiogenesis. Both receptors are selectively expressed by vascular endothelial cells and are strikingly increased in tumor vessels. We used a specific antibody to localize VEGFR-2 (FLK-1, KDR) in microvascular endothelium of normal mouse kidneys and in the microvessels induced by the TA3/St mammary tumor or by infection with an adenoviral vector engineered to express VPF/VEGF. A pre-embedding method was employed at the light and electron microscopic levels using either nanogold or peroxidase as reporters. Equivalent staining was observed on both the luminal and abluminal surfaces of tumor- and adenovirus-induced vascular endothelium, but plasma membranes at interendothelial junctions were spared except at sites connected to vesiculovacuolar organelles (VVOs). VEGFR-2 was also localized to the membranes and stomatal diaphragms of some VVOs. This staining distribution is consistent with a model in which VPF/VEGF increases microvascular permeability by opening VVOs to allow the transendothelial cell passage of plasma and plasma proteins.

A technique for extracting physiological parameters and the required input function simultaneously from PET image measurements: theory and simulation study

Positron emission tomography (PET) is an important tool for enabling quantification of human brain function. However, quantitative studies using tracer kinetic modeling require the measurement of the tracer time-activity curve in plasma (PTAC) as the model input function. It is widely believed that the insertion of arterial lines and the subsequent collection and processing of the biomedical signal sampled from the arterial blood are not compatible with the practice of clinical PET, as it is invasive and exposes personnel to the risks associated with the handling of patient blood and radiation dose. Therefore, it is of interest to develop practical noninvasive measurement techniques for tracer kinetic modeling with PET. In this paper, a technique is proposed to extract the input function together with the physiological parameters from the brain dynamic images alone. The identifiability of this method is tested rigorously by using Monte Carlo simulation. The results show that the proposed method is able to quantify all the required parameters by using the information obtained from two or more regions of interest (ROI's) with very different dynamics in the PET dynamic images. There is no significant improvement in parameter estimation for the local cerebral metabolic rate of glucose (LCMRGlc) if the number of ROI's are more than three. The proposed method can provide very reliable estimation of LCMRGlc, which is our primary interest in this study.

A novel lncRNA, LUADT1, promotes lung adenocarcinoma proliferation via the epigenetic suppression of p27

Long noncoding RNAs (lncRNAs) are known to regulate the development and progression of various cancers. However, few lncRNAs have been well characterized in lung adenocarcinoma (LUAD). Here, we identified the expression profile of lncRNAs and protein-coding genes via microarrays analysis of paired LUAD tissues and adjacent non-tumor tissues from five female non-smokes with LUAD. A total of 498 lncRNAs and 1691 protein-coding genes were differentially expressed between LUAD tissues and paired adjacent normal tissues. A novel lncRNA, LUAD transcript 1 (LUADT1), which is highly expressed in LUAD and correlates with T stage, was characterized. Both in vitro and in vivo data showed that LUADT1 knockdown significantly inhibited proliferation of LUAD cells and induced cell cycle arrest at the G0–G1 phase. Further analysis indicated that LUADT1 may regulate cell cycle progression by epigenetically inhibiting the expression of p27. RNA immunoprecipitation and chromatin immunoprecipitation assays confirmed that LUADT1 binds to SUZ12, a core component of polycomb repressive complex 2, and mediates the trimethylation of H3K27 at the promoter region of p27. The negative correlation between LUADT1 and p27 expression was confirmed in LUAD tissue samples. These data suggested that a set of lncRNAs and protein-coding genes were differentially expressed in LUAD. LUADT1 is an oncogenic lncRNA that regulates LUAD progression, suggesting that dysregulated lncRNAs may serve as key regulatory factors in LUAD progression.

Adipose stromal cells-secreted neuroprotective media against neuronal apoptosis

Transplantation of pluripotent adipose stem/stromal cells (ASC) alleviates tissue damage and improves functional deficits in both stroke and cardiovascular disease animal models. Recent studies indicate that the primary mechanism of ASC-induced repair may not be directly related to tissue regeneration through differentiation, but rather through paracrine mechanisms provided by secreted pro-survival and repair-inducing trophic factors. In this study, we have found that ASC-conditioned medium (ASC-CM) potently protected cerebellar granule neurons (CGN) from apoptosis induced by serum and potassium deprivation. Neural cell protection was mostly attributable to activated caspase-3 and Akt-mediated neuroprotective pathway signaling. Specific neutralization of neurotrophic factor activity demonstrated that serum and potassium deprivation-induced Akt-mediated neuroprotection and caspase-3-dependent apoptosis were mainly modulated by IGF-1. These data suggest that of the many neuroprotective factors secreted by ASC, IGF-1 is the major factor that mediates protection against serum and potassium deprivation-induced CGN apoptosis. This study establishes a mechanistic basis supporting the therapeutic application of ASC for neurological disorders, specifically through paracrine support provided by trophic factor secretion.

Reinterpretation of endothelial cell gaps induced by vasoactive mediators in guinea-pig, mouse and rat: many are transcellular pores

1. In response to vascular permeabilizing agents, particulates circulating in the blood extravasate from venules through endothelial cell openings. These openings have been thought to be intercellular gaps though recently this view has been challenged. 2. To define the precise location of endothelial cell gaps, serial section electron microscopy and three-dimensional reconstructions were performed in skin and cremaster muscle of guinea-pigs, mice and rats injected locally with agents that enhance microvascular permeability: vascular permeability factor, histamine or serotonin. Ferritin and colloidal carbon were injected intravenously as soluble and particulate macromolecular tracers, respectively. 3. Both tracers extravasated from venules in response to all three permeability enhancing agents. The soluble plasma protein ferritin extravasated primarily by way of vesiculo-vacuolar organelles (VVOs), interconnected clusters of vesicles and vacuoles that traverse venular endothelium. In contrast, exogenous particulates (colloidal carbon) and endogenous particulates (erythrocytes, platelets) extravasated from plasma through transendothelial openings. 4. Serial electron microscopic sections and three-dimensional reconstructions demonstrated that eighty-nine of ninety-two openings were transendothelial pores, not intercellular gaps. Pore frequency increased 3- to 33-fold when carbon was used as tracer. 5. The results demonstrate that soluble and particulate tracers extravasate from venules by apparently different transcellular pathways in response to vasoactive mediators. However, some pores may derive from rearrangements of VVOs.

Estimation of local cerebral protein synthesis rates with L-[1-11C]leucine and PET: methods, model, and results in animals and humans

We have estimated the cerebral protein synthesis rates (CPSR) in a series of normal human volunteers and monkeys using L-[1-11C]leucine and positron emission tomography (PET) using a three-compartment model. The model structure, consisting of a tissue precursor, metabolite, and protein compartment, was validated with biochemical assay data obtained in rat studies. The CPSR values estimated in human hemispheres of about 0.5 nmol/min/g agree well with hemispheric estimates in monkeys. The sampling requirements (input function and scanning sequence) for accurate estimates of model parameters were investigated in a series of computer simulation studies.

Different pathways of macromolecule extravasation from hyperpermeable tumor vessels

Tumor microvessels are hyperpermeable to plasma proteins, a consequence of tumor cell-secreted vascular permeability factor/vascular endothelial growth factor (VPF/VEGF). However, the pathways by which macromolecules extravasate from tumor vessels have been little investigated. To characterize tumor vessels more precisely and to elucidate the pathways by which macromolecules extravasated from them, we studied two well-defined, VPF/VEGF-secreting murine carcinomas, MOT and TA3/St. Whether grown in ascites or solid form, MOT tumors induced large, pericyte-poor "mother" vessels whose lining endothelium developed fenestrae that involved 1.8-5.6% of the surface. Fenestrae developed in parallel with markedly reduced endothelial cell vesiculo-vacuolar organelles (VVOs). TA3/St tumors, which secreted more VPF/VEGF than MOT tumors, elicited mother vessels with unchanged VVOs and without fenestrae. In both tumors, a plasma protein tracer, ferritin, extravasated through VVOs and in MOT tumors ferritin also extravasated through fenestrae. Endothelial gaps were not observed in either tumor. Thus, not all VPF/VEGF-secreting tumors induce fenestrated endothelium. Also, VVOs provide an internal store of membrane that can be transferred to the endothelial cell surface to provide the substantial increase in plasma membrane necessary for mother vessel formation in MOT tumors. Such transfer was apparently unnecessary in TA3/St tumors in which extensive early endothelial cell division provided the increased plasma membrane necessary for forming mother vessels.

Hemostatic state and atrial fibrillation (the Framingham Offspring Study)

Atrial fibrillation (AF) is strongly associated with thromboembolic complications, although the mechanism for the increased risk has not been fully explained. To determine whether AF might be associated with a hypercoagulable state, we studied hemostatic factors in subjects with or without AF in the Framingham Heart Study. In 3,577 subjects, we measured fibrinogen, von Willebrand factor antigen, tissue plasminogen activator (tPA) antigen, and plasminogen activator inhibitor-1 antigen. Forty-seven subjects had AF at the index clinic examination and 15 had AF on a prior examination, but not on the current examination. Before matching, the 47 subjects with prevalent AF had higher levels of fibrinogen, von Willebrand factor, and tPA antigen than those without AF, all p < or =0.03. Compared with 167 referent subjects matched for age, sex, and other risk factors, those with AF had higher tPA antigen levels than those without AF, 1 1.8 +/- 4.0 ng/ml versus 10.5 +/- 3.9 ng/ml (p = 0.04). However, when further stratified according to their cardiovascular disease status, the differences in hemostatic factors were no longer significant. We conclude that the prothrombotic profile associated with AF was explained by the risk factors of the subjects and the presence of cardiovascular disease. Nonetheless, the hemostatic changes may contribute toward the propensity for thromboembolic complications in AF. Further prospective studies are needed to evaluate whether measurement of these and other hemostatic factors will identify patients with AF who are at increased risk for thromboembolic complications, and who may therefore benefit from more intensive therapy.